A method and a device for joining two plastic pipe-like elements are generally known. The joining of two plastic elements usually needs to take place in a liquid- and/or gastight manner. In this connection, the liquid- and/or gastight joining of two pipe sections, for example, thermoplastic (PVC) pipe sections for use in sewage pipes, rainwater pipes, gas pipes, drainpipes etc. are of particular consideration. In view of the large number of applications it will be apparent that liquid- and/or gastight pipe sections may be quite different from each other, not only as regards their shape but also as regards their technical characteristics, since generally each application has its specific requirements (relating to technique and shape). Thus pipe sections made of various plastic materials, of various shapes and of various material thicknesses are known.
A drawback of a known method and a known device is that, in the case of manually joined pipe sections, a constant quality of the joint as regards its liquid- and/or gastightness is not always achieved, while the (production) costs involved are often very high, and that, when the work is carried out by mechanical means (e.g. injection molding), it is not possible to obtain the required flexibility for joining different kinds of plastic elements (in particular different as to shape and diameter) at acceptable cost.
The present invention particularly relates to a method and a device for Joining at least two plastic elements in a liquid- and/or gastight manner, whereby an edge of a first plastic element is at least partially placed in an opening of a second plastic element, the edge of the first plastic element being folded using pressure means over an edge of the opening of the second plastic element under plastic deformation.
Such a method is known from U.S. Pat. No. 3,798,097 to Mendenhall. This known method of joining a plastic tube to the side of a plastic pipe to make a branched conduit, comprises the steps of:
forming a hole in the side of a pipe smaller than the size of the tube; PA1 softening the pipe around the hole by means of a hot oil bath; PA1 deforming the pipe outwardly around the hole to form an outwardly projecting flange, while expanding the hole to a size sufficient to receive the tube; PA1 softening one end portion of the tube to a temperature at which it is plastically deformable and inserting the softened end portion into the hole; PA1 plastically deforming said the end portion into an enlarged lip abutting the inside of the pipe around the hole; PA1 hardening the end in the deformed condition; PA1 applying PVC solvent cement between the abutting portions of the tube and pipe; PA1 applying pressure (using an inflatable balloon) to the abutting portions to press them together during bonding; and PA1 relieving the pressure after the tube and pipe are bonded together.
A drawback of the method disclosed in U.S. Pat. No. 3,798,097 is that the pressure exerted by the inflatable balloon on the above-mentioned abutting portions to press them together, is inadequate to provide an effective liquid- and/or gastight bond between the tube and the pipe. A further drawback of this method is that the use of PVC solvent cement as a bonding material is needed. This not only renders the method uneconomical and difficult to apply, but the bond also deteriorates after a period of time. This has negative effects on the quality of the bond between the tube and the pipe. A further drawback is that the tube and the pipe can only be joined at an angle of 90.degree. limiting the applicability of this method. Still a further drawback is that the method of this U.S. patent is complicated and expensive in view of the use of the different materials and steps, e.g. expanding mandril, inflatable balloon, hot oil bath, PVC solvent cement etc.